Wash the apple, core it, cut it in half. Cut the apple into thin slices.
Place the sliced apples in a bowl. Add 1 teaspoon of olive oil, honey, and ground coriander. Stir well so that each wedge is covered with a honey-oil mixture.
Place in the microwave for 30 seconds. The apples will become soft.
For the sauce, mix the remaining butter with the mustard and lime juice.
Toast rye bread in a toaster or in a dry frying pan.
Put apples on the bread in one layer.
Put a piece of mackerel on the apples (remove bones, if any).
Pour the sauce over the fish, garnish with mint leaves and serve.